RESCAN is an actinic patterned EUV mask metrology tool based on coherent diffraction imaging. An image of the reticle is reconstructed from recorded diffraction patterns using a phase retrieval algorithm. As semiconductor manufacturing has moved to EUV lithography to meet the next technology node, accurate photomask metrology with resolution in the nanometer range is crucial for high production yield. To find the optimal reconstruction strategy to achieve the highest resolution, sensitivity and reconstruction speed in RESCAN, we compared three algorithms. We demonstrate that, for the current setup, the best approach is the difference map algorithm.
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